The invention relates to electrostatography, and more particularly to improvements in electrostatographic imaging surfaces.
In the art of electrostatographic copying, as originally disclosed by Carlson in U.S. Pat. No. 2,297,69l, and as further described in many related patents in the field, an electrostatographic imaging surface containing a photoconductive insulating layer is first given uniform electrostatic charge in order to sensitize its entire surface. The surface is then exposed to an image of activating electromagnetic radiation such as light, X-ray, or the like, which selectively dissipates the charge in the illuminated areas of the photoconductive insulator while leaving a charge pattern in the non-illuminated areas. The charge pattern is then developed and made visible by depositing finely divided marking material (referred to in the art as "toner") on the surface of the photoconductive insulating layer. Where reusable photoconductive insulating material is used, the visible image formed by the toner is transferred to a second surface, such as a sheet of paper, and fixed in place thereon to form a permanent visible reproduction of the original image. Where a nonreusable photoconductive insulating material is used, the toner particles are directly fixed in place on the surface of the nonreusable insulating material thereby eliminating the transfer step from the previous process.
Such a charge pattern may also be developed by a liquid developer. In one known liquid development process a charge pattern is established on an imaging surface and is developed by a liquid development process wherein the liquid developer is presented to the charge pattern by an applicator which has a surface comprising raised portions (lands) and recesses (valleys) adapted to contain liquid developer between the raised portions. The liquid developer is drawn to the imaging surface in image configuration by the electrostatic forces of the charge pattern.
A preferred method for the liquid development of electrostatic charge patterns is shown in British Patent 880,597. In this method the imaging surface may be a cylindrical member which is cyclically imaged with a charge pattern which is developed and the developed image transferred to a record receiving means after which the imaging surface is cleaned in preparation for subsequent such cycles.
Imaging surfaces which are suitable for use with either the toner development or liquid development of charge patterns are desirably photoconducting insulating layers which are sufficiently rigid to support a developed image. If used in a cyclic mode, as described above, it can also be desirable to use imaging surfaces which are somewhat flexible and which may be easily cleaned. In any event the surface of the layer should be sufficiently smooth that the quality of the developed image is not marred. Examples of such imaging surfaces are described in U.S. Pat. Nos. 3,552,848; 3,62l,248; 3,685,989; 3,697,265 and 3,752,691.
While ordinarily capable of producing good quality images, the imaging surface of the prior art can be improved in certain areas. Imaging surfaces have been found to have surface defects in the form of "hills" or "bumps" which may protrude as much as 100 microns above the imaging surface. Such defects are thought to be formed during the plating process used to coat the photoconductive material onto a substrate. They are often found on imaging surfaces which are commonly used in both toner and liquid development of charge patterns.
Such surface defects do not ordinarily adversely affect the quality of toner developed images, however, they are found to detract to a much greater degree from the quality of liquid developed charge patterns. In the case of the liquid development of charge patterns on such an imaging surface, the surface defects cause at least two undersirable imperfections in the developed image. The liquid developer gathers in a circle around the defect so that it transfers as a circle onto the image receiving surface. This is commonly known in the art as the "halo effect". A second undesirable imperfection occurs after a plurality of copies have been made by known liquid development methods as described, for instant, in British Pat. No. 880,597. When a liquid developer applicator is rotated in contact with an imaging surface, the applicator will tend to strike against the imperfections on the imaging surface. The larger imperfections and those having a steep profile are sometimes broken off. The resulting roughened area or hollow tends to collect liquid developer which appears as an unwanted spot in the developed image whether the developed image remains on the imaging surface or is transferred to an image receiving means.
It has been proposed in a copending U.S. patent application, Ser. No. 701,764, to reduce such troublesome surface defects by contacting the imaging surface with a smoothing means which "cold-flows" the defects to substantially reduce their height to less than about 5 microns. Such a method has been found particularly satisfactory when used with metal or metal-like imaging surface materials. Upon occasion, however, the surface defects have a sharp profile which can be inadvertently broken off by such smoothing means to form the undesirable roughened areas or hollows described above. In addition, smoothing or cold flow techniques are not always completely successful when used with non-metallic photoreceptor materials which are less compatible with a cold flowing process.
It is, therefore, an object of the invention to provide a method for improving liquid developing characteristics of a non-metallic xerographic imaging surface having surface irregularities in excess of about 5 microns.
The above object is obtainable in accordance with the present invention through initially treating the imaging surface by contacting with smoothing and abrading means having a patterned surface at the points or lines of contact, and slidably moving the smoothing and abrading means alone or in combination with and relative to the xerographic imaging surface in the presence of an interposed fluid bearing.
Such interposed fluid bearing can usefully be of a hydrodynamic or hydrostatic nature depending upon the nature and shape of the photoreceptor.